Sensitization of silver bromoiodide emulsions with amidophosphoric acid polyethyleneglycol esters



United States Patent 4 claim. an. 96-66) ABSTRACT @F THE DESCLGSURE Increasing the effective sensitivity of photographic silver bromoiodide emulsions by carrying out the development of these emulsions while they are in contact with a sensitizing concentration of certain amidophosphoric acid polyethyleneglycol esters.

A number of methods have been described for increasing the sensitivity of photographic silver halide emulsions, other than methods of optical or spectral sensitization which involve the incorporation of certain colored compounds or dyes in the emulsion-s. The incorporation of such dyes in the emulsions increases the optical range of sensitivity, and for this reason such dyes are commonly referred to as optical or spectral sensitizing dyes. It is also well known to increase the sensitivity of photographic emulsions by addition of sulfur compounds capable of eacting with silver salts to form silver sulfide, or with reducing agents (compounds of these types are also naturally present in gelatin), or with salts of gold or other noble metals, or with combinations of two or more of the aforementioned compounds generally known as chemical sensitizers. Such chemical sensitizers are believed to react with the silver halide to form, on the surface of the silver halide, minute amounts of silver sulfide or of silver or of other noble metals, and these processes are capable of increasing the sensitivity of emulsions by very large factors. The process of chemical sensitization, however, reaches a definite limit beyond which further addition of sensitizer, or of further digestion with, the sensitizer present, merely increases the fogging of the photographic emulsion and leaves it with constant or decreasing sensitivity.

Other chemical sensitizers are higher polyethylenglycols having a molecular weight of at least 1500. Lower polyethylenglycols have no or only very small effect on the sensitivity of silver halide emulsions. While the higher polyethylenglycols have a considerable or remarkable sensitization effect, the utility of such compounds is limited by the effect that they cause marked increases in the fog levels of silver halide emulsions. It is known that such fog level increase cannot be controlled by the addition of antifoggants to the emulsion.

It is among the objects of the invention to increase the general sensitivity or speed of silver halide emulsion layers. A further object is to provide photographic silver halide emulsions and emulsion layers having an increased general sensitivity without concomitant increases in fog levels. Other objects will be apparent from the following description of the invention.

By the term general sensitivity or increasing of the general sensitivity it is to be understood the increasing of the sensitivity of photographic emulsions equally through the whole region of the spectrum. By the term spectral sensitivity is to be understood the sensitivity of the photographic emulsion to light of a certain region of 3,385,704 Patented May 28, 1968 the visible spectrum which is given by the inherent sensi tivity of silver halides or which is amplified by the addition of so-called optical and spectral sensitizers.

The foregoing objects are attained by the use of amidophosphoric acid polyethylenglycol esters. These products increase the general sensitivity of silver halide emulsions, the silver halide of which consists of at least mol percent silver bromide. Preferred are silver bromo iodide emulsions containing between 0.5 and 10 mol percent silver iodide.

The said esters can be obtained by esterifying monoamido phosphoric acid derivatives of the following Formula I with polyethylene glycols of the following Formula II:

wherein:

R represents an (1) alkyl group preferably with l to 12 carbon atoms;

(2) an aryl group such as naphthyl or preferably a radical of the benzene series in which the phenyl group may be substituted by radicals capable of reacting with polyalkylen glycols. Suitable substituents are alkyl groups with up to 12 carbon atoms, preferably with l to 6 carbon atoms, halogen atoms such as chlorine and bromine, alkoxy groups with up to 6 carbon atoms and the like; or

(3) aralkyl such as benzyl or phenylethyl, the benzene radicals of which may be substituted with the substituents referred to hereinbefore.

R stands for hydrogen or R or R and R together represent the ring members necessary to complete a 5- or 6-rnembered heterocyclic ring, such as a morpholidine ring, a pyrollidine ring or a piperidine ring.

Y stands for a halogen atom preferably chlorine, or an all-:oxy group with preferably up to 5 carbon atoms;

n is an integer between 2 and 100, preferably between 3 and 50, more preferably 3-35.

The following amido-phosphoric acid derivatives of Formula I are particularly useful for the preparation of the amide-phosphoric acid polyethylenglycol esters:

ence of acid-binding agents, in particular amines such as pyridine, at temperatures of about to C. In the case of amidophosphoric acid alkyl esters as starting compounds the reaction is performed in the presence of ester interchange catalysts such as sodium or sodium alcoholate at temperatures of about 90 to 150 C. The polyalkylene glycols can be used in quantities of about 1 to 2 mols per mol of phosphoric acid derivative.

The csterification products obtained in the reaction of the above components have the following formula:

III "I where R R and n, have the meaning given above, m=0 or n and X has a value of between 1 and 100, preferably 1-5; R stands for hydrogen, alkyl having up to carbon atoms, preferably between 1 and 5 carbon atoms, or an acyl group, preferably an acyl group derived from a lower aliphatic carboxylic acid having up to 5 carbon atoms, such as acetyl, propionyl or valeryl group.

The degree of condensation of the polyglycol esters, that is the integer X in Formula III, may be influenced by varying the reaction time, the reaction temperature and the proportions of the reaction components. Particularly advantageous are water-soluble amidophosphoric polyglycol esters with a molecular weight of about between 800 and 3000.

In the following examples a number of condensation products are separately described.

(I) The condensation product from 1 mol hexaethyleneglycol and 1 mol N,N-diethylamido-phosphoric acid dichloride wherein X is 3.8.

Preparation of the compound.l9 g. of N,N-diethylphosphoric acid amide-dichloride are added in portions at temperatures between 0 and 5 C. while stirring to a mixture of 31.2 g. of pyridine and 28.2 g. of hexaethylene glycol. The mixture is left standing for 5 hours at room temperature and is then poured onto ice, acidified with l-N-sulphuric acid and extracted with methylene chloride. After drying with potash, the methylene chloride is completely evaporated. There are obtained 39 g. of a syrupy amber-colored substance.

(II) The condensation product of 1 mol nonaethylene glycol and 1 mol N,N-diethylarnido-phosphoric acid dichloride wherein X is 4.9.

Preparation of the compound.-4l.2 g. of nonaethylene glycol, 31.2 g. of pyridine and 19 g. of N,N-diethyl phosphoric acid amidedichloride are reacted and worked up in the manner described above. There are obtained 45 g. of a semi-solid, brown-colored substance, which is diluted with water to a 10% solution and urified with activated carbon.

(III) The condensation product of 1.5 mol hcxaethyleneglyool and 1 mol N-methyl-N-phenylamidophosphoric acid dichloride wherein X is 1.8.

Preparation of the compound-The preparation is similar to that of compound (I), by reaction of 28.2 g. of hexaethylene glycol, 312 g. of pyridine and 22.4 g. of N-methyl-N-phcnyl phosphoric acid amide dichloride.

4. There are obtained 39 g. of a brown-colored semi-solid substance, which is purified with activated carbon.

(IV) The condensation product of 1 mol nonaethyleneglycol and 1 mol N-methyl-N-phenylamido-phosphoric acid dichloride wherein X is 7.3.

Preparation of the compound.-41.4 g. of nonaethylene glycol, 31.2 g. of pyridine and 22.4 g. of N-methyl-N- phenyl phosphoric acid amidedichloride are reacted in a manner analogous to Compound I. There are formed 50 g. of a brown-colored semi-solid substance, which is diluted with water and decolorised with activated carbon.

(V) The condensation product of 1.1 mol octaethyleneglycol and 1 mol N-propylamido-phosphoric acid diethyl ester wherein X is 2.3.

Preparation of the compound.-1 mol of propylamidophosphoric acid diethyl ester is heated with approximately a 10% molar excess of octaethylene glycol in the presence of reesterification catalysts, such as sodium or sodium alcoholate, for several hours at to C. The ethyl alcohol that is liberated is constantly distilled oil in vacuo and the residue can be used for the purpose of the present invention.

(VI) The condensation product of 1 mol polyethyleneglycol containing approximately 30 to 35 ethylene oxide groups and 1.1 mol N,N-diisobutylamidophosphoric acid dichloride where X is 3.4.

This compound is prepared in an analogous manner.

(VII) The condensation product of 1 mol octadeca ethyleneglycol and 1 mol N,N-diethylamido-phosphoric acid dichloride where X is 7.3. Prepared as described above.

(VIII) The condensation product of 1 mol octadecaethyleneglycol and 1 mol N-methyl-N-phenylamido-phosphoric acid dichloride wherein X is 2.7. Prepared as described above.

For the above purpose it is also suitable to use derivatives of the above amidophosphoric acid polyglycol esters, obtainable by reacting their hydroxyl end groups with etherifying or esterifying agents such as orthoformic acid esters, acetic anhydride, succinic acid anhydride, maleic acid anhydride or isocyanates or isothiocyanates.

The silver halide emulsions to be used according to the invention generally consist of silver bromide emulsions which may contain silver chloride and iodide in quantities of less than 50 mols percent calculated on the silver bromide. The sensitizers of the present invention are particularly suitable for use in silver iodo-bromide emulsions.

The preparation of photographic silver halide emulsions includes 3 separate steps:

(1) emulsification and physical ripening which is also called Ostwald ripening;

(2) the freeing of the emulsion of excess water soluble salts, usually by Washing with Water and drying;

(3) the after ripening which is also called chemical ripening to obtain increased emulsion speed or general sensitivity.

The sensitizers of the present invention can be added to the emulsion before, during or after the chemical ripening or they can be added immediately prior to the casting.

The particular quantity of the sensitizers of the invention used in a given emulsion can vary, depending upon the effects desired, the silver content of the emulsion, the silver halide composition etc. Generally they are added in amounts of 50 mg, to 1 g., preferably 10 to 200 mg. per mol of silver halide.

The compounds are also effective when they are added to the developer solution, in which case they are preferably used in quantities of between 100 mg. to 1 g. preferably 30 and 600 mg. per liter of the aqueous developer bath.

The sensitizers can be dissolved in Water or a solvent miscible with water or a mixture of water and Water-miscible solvents, and added in this form to the emulsion. The solvent is not critical and should be selected so that it should have no harmful effect on the photographic properties of the silver halide emulsion.

The optimum amount for any sensitizer of the present invention can be determined for any particular emulsion by running a series of comparison tests in which the quantity of the sensitizer is varied over a given range. Exposure of the emulsion containing the sensitizer in a manner well known and measuring of the sensitivity in conventional apparatuses will reveal most advantageous concentrations. Such technic is well understood by those skilled in the art.

The photographic emulsion in which the sensitizers according to the invention are used, can be chemically sensitized by any of the known procedures. They can be sensitized, for example, with sulfur compounds as referred to e.g., in the book The Theory of the Photographic Process by Mees (1954), pp. 149-16l.

The emulsions can also be chemically sensitized with salts of a noble metal such as gold, ruthenium, rhodium, palladium, iridium and platinum, which salts are used in amounts below that which produce any substantial fog. Representative compounds are ammonium chloropalladate, potassium chloroplatinate, potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and the like. The emulsions can be sensitized with reducing agents, stannous salts or polyamines and the like. The emulsions can also be optically sensitized with cyanine, merocyanine or rhodacyanine dyes.

The emulsions can be stabilized with any of the known stabilizers, such as mercury compounds, triazoles, for example, mercapto phenyl triazoles or azaindenes as described, for example, by Birr in Z.wiss.phot. vol. 47 (1952) pp. 2 to 28. The silver halide emulsions layers may contain as binding agent any suitable film-forming and water permeable colloid, such as gelatin, which can be replaced partially with products like alginic acid and derivatives thereof such as salts preferably with alkali metals, esters with lower aliphatic alcohols, or amides. The gelatin can also be partly replaced by polyvinyl alcohol, polyvinyl pyrrolidone starch, carboxymethyl cellulose and the like.

The following examples will serve to illustrate more fully the manner of sensitizing photographic silver halide emulsions with the sensitizers of the present invention.

EXAMPLE 1 An ordinary photographic silver bromo iodide emulsion, for example, a gold sensitized emulsion containing 0.45 mol silver halide consisting of 94 mol percent of silver bromide and 6 mol percent of silver iodide per kg. of casting solution, was divided into several portions. The emulsion furthermore contains the usual quantitles of an optical sensitizing dye such as a stabilizer such as 250 mg. of 5-rnethyl-7-hydroxy- 2,3,4-triazoindolizine, a hardening agent as, for example,

disclosed in German Patent No. 872,153 and a wetting agent such as saponine (30 ml. of a 7.5 aqueous solution of saponine per kg. of emulsion are added).

Amidophosphoric acid polyethylenglycol esters of the type obtained in the above examples were then added in aqueous solution or in solution in an aqueous medium such as a mixture of water and lower aliphatic alcohols,

in the following amounts:

Sample A.Standard, no additive;

Sample B.Comparison test, 160 mg. of nonaethylene glycol;

Sample C.--16O mg. of condensation product (II);

Sample D.200 mg. of condensation product (IV); Sample E.--200 mg. of condensation product (VII); Sample F.-200 mg. of condensation product (VIII).

The various portions of emulsions were then coated on a transparent support such as cellulose acetate and then dried.

The dried layers were exposed behind a grey test wedge in a sensitometer and developed for 10 minutes at 18 C. in a developer of the following composition:

G. Sodium sulfite sicc. 70 Borax 7 Hydroquinone 3.5 Monomethyl-p-aminophenol 3.5 Sodium citrate 7 Potassium bromide 0.4

Made up to 1 liter with water.

The relative speed as compared with the standard sample A, 'y and fog for each of the coatings are then measured. The results are given in the following table:

TABLE 1 Relative speed Gamma Fog 1 Standard.

The relative speed values are given in DIN units. As to DIN we refer to the book by C. B. Neblette, 5th edition, published by Macmillan Company, London, 1952, pp. 264467.

EXAMPLE 2 Two strips of the photographic standard material (sample A of Example 1) were exposed behind a grey test wedge. One of these strips, sample G, was developed for 10 minutes at 18 C. in a developer composition specified in Example 1; the other strip (sample H) was developed in the same developer composition which, however, additionally contained 400 mg. of condensation product of compound VIII. The further processing of the samples was identical. The results are given in the following Table 2.

TABLE 2 Sample Relative speed Gamma Fog Standard.

The relative speed values are as mentioned in Example 1.

We claim:

1. In the process of developing an exposed silver iodobromide emulsion having a silver iodide content of not more than 10 mol percent based on the total silver halide, the improvement according to which the development is carried out while the emulsion is in contact with a sensitizing concentration of a compound having the formula wherein:

R stands for a radical of the group consisting of alkyl, naphthyl, a radical of the benzene series, benzyl and phenylethyl;

R represents hydrogen, alkyl, naphthyl, a radical of the benzene series, benzyl or phenylethyl; or

of which consists of a mixture of silver bromide and up 10 to 10 mol percent silver iodide, the said silver halide emulsion layer also having a sensitizing amount of an amidophosphoric acid polyethylenglycol ester of the formula wherein:

R stands for a radical of the group consisting of alkyl, naphthyl, a radical of the benzene series, benzyl and phenylethyl;

R represents hydrogen, alkyl, naphthyl, a radical of the benzene series, benzyl or phenylethyl; or R and R together represent the ring members necessary to complete a 5- or 6-membered heterocyclic ring; 11 is an integer between 2 and 100; m is an integer between 0 and 100; R stands for hydrogen, alkyl or acyl; and X has a value between 1 and 100. 3. The combination of claim 1 in which m is equal to n and is between 3 and 50.

4. The combination of claim 2 in which m is equal to n and is between 3 and 50.

References Cited UNITED STATES PATENTS 2,870,042 1/ 1959 Chance et. al. 8l16.2 3,256,249 6/1966 Vogt et. a1. 260928 3,190,752 6/ 1965 Hayakawa 96-407 NORMAN G. TORCHIN, Primary Examiner.

J. H. RAUBITSCHEK, R. E. FIGHTER,

Assistant Examiners. 

